1. Field of the Invention
The present invention relates to an improvement in a light emitting diode and more specifically to a light emitting diode which converts a natural color of light from a light emitting element chip into a soft, intermediate pastel color.
2. Description of the Prior Art
A conventional practice to produce an intermediate color of light involves simultaneously causing two or more light emitting element chips to emit different colors of light and mixing them. An example light emitting diode of this kind is a surface mount type light emitting diode 1 which has two light emitting element chips 3, 4 that produce two different colors of light, as shown in FIG. 1. This light emitting diode 1 has a glass epoxy substrate 2 forming a base, two light emitting element chips 3, 4 mounted on the substrate to emit different colors of light, and a resin sealing member 5 covering the light emitting element chips 3, 4 from above. On the upper surface of the glass epoxy substrate 2 are provided cathode electrodes 6a, 6b for securely holding the two light emitting element chips 3, 4 and anode electrodes 8a, 8b connected to the light emitting element chips 3, 4 through bonding wires 7.
In the light emitting diode 1, when the two light emitting element chips 3, 4 are made from a blue color chip and a red color chip, respectively, violet light can be produced by causing the two chips to emit light simultaneously and mixing the different colors of emitted light.
A light emitting diode 10 is also known which has three light emitting element chips mounted thereon and mixes multiple colors to produce a desired color of light, as shown in FIG. 2. This light emitting diode 10 comprises three light emitting element chips 12, 13, 14 mounted on a base 11 that emit light in red, blue and green, respectively, electrode terminals 15, 16, 17 connected to the light emitting element chips 12, 13, 14, respectively, and a bullet-shaped resin sealing member 18 covering the light emitting element chips 12, 13, 14 from above. The light emitting diode 10 of this construction can produce light of almost any color by combining the three light emitting element chips 12, 13, 14 that emit light in red, blue and green (see Masakazu Matsumoto, xe2x80x9cElectronic Display,xe2x80x9d from Ohmsha Co., Ltd., p213, FIGS. 6 and 20, Jul. 7, 1995).
In either of the light emitting diodes 1, 10 described above, to produce an intermediate color of light requires two or more light emitting element chips that emit different colors of light. This necessarily increases the size of the package of the light emitting diode and requires a control circuit to individually control the mounted light emitting element chips, thus complicating the control method. Depending on the kinds of light emitting element chips combined, an optimum balance in brightness among different colors may not be able to be established. For example, if one of the light emitting element chips to be used in combination has a low brightness, an adjustment must be made to match other light emitting element chips to the low-brightness chip, giving rise to a problem that performances of high-luminance light emitting element chips cannot be fully exploited.
The light emitting diodes 1, 10 described above also have a problem of a large current consumption resulting from the need to make a plurality of light emitting element chips produce light simultaneously.
An object of the present invention is to provide a light emitting diode capable of producing a variety of intermediate colors of light with a single light emitting element chip.
Another object of the present invention is to provide a small, inexpensive light emitting diode.
Still another object of the present invention is to provide a light emitting diode which consumes a small amount of current in the light emitting element chip and which has no need to control the current.
According to one aspect, the present invention provides a light emitting diode which comprises: a substrate; a light emitting element chip mounted on the substrate; a wavelength conversion material to receive light from the light emitting element chip and change wavelengths of the received light; and a wavelength absorbing material to receive the light from the light emitting element chip and the wavelength conversion material and absorb a part of the wavelengths of the received light.
The substrate is formed with electrodes, which are connected to the light emitting element chip.
The wavelength conversion material is made from, for example, fluorescent particles and the wavelength absorbing material is made from, for example, coloring particles.
It is preferred that the wavelength conversion material and the wavelength absorbing material be dispersed in a scatteringly distributed condition in a cover member enclosing the light emitting element chip.
The cover member may be made from a light transmitting resin material.
Because the resin material is mixed with the fluorescent particles for producing light with a wider range of wavelength and with coloring particles for absorbing a desired wavelength range, it is possible to produce a soft, intermediate, pastel color of light based only on the color of light emitted by a single light emitting element chip.
According to another aspect of the present invention, the fluorescent particles are made from yttrium aluminum garnet (YAG).
Because this invention uses yttrium aluminum garnet (YAG) for the fluorescent particles, a wide range of wavelengths, 400 nm to 700 nm, can be produced stably and efficiently by exciting the fluorescent particles.
According to still another aspect of the present invention, the coloring particles are made from a dye which absorbs a part of wavelengths of light from the light emitting element chip and a part of wavelengths of light that were changed by the fluorescent particles.
Because this invention uses a dye for the coloring particles, it is possible to produce a soft, intermediate, pastel color of light with low cost.
According to a further aspect of the present invention, the light emitting element chip is a blue light emitting diode element formed of a gallium nitride compound semiconductor.
These and other features and advantages of the present invention will be described in more detail by referring to the accompanying drawings.